Pergamon NanoStractured Materials, Vol. 12, pp. 155-158, 1999 Else&r Science. Ltd PII SO%59773(99)00087-Z 8 1999 Acta Metallurgica Inc. Printed in the USA. All rights reserved 09659113l99l.$-see front matter IRON NANOPARTICLES IN X AND Y ZEOLITES K. LBdrl, H.K. Beyerl, G. Onyestyhk2, B J. Jiinsson3, L.K. Varga4, S. Pronier5 * Institute of Isotope and Surface Chemistry, Budapest, P.O.B. 77, H-1525, Hungary 2 Institute of Chemistry, Budapest, P.O.B. 17, H-1525, Hungary 3 Dept. Condensed Matter Physics, Royal Inst. Technology, S-10044 Stockholm, Sweden 4 Institute of Solid State Physics, Budapest, P.O.B. 49, H-1525, Hungary 5 LACCO, URA CNRS 350, Universite de Poitiers, F-86022 Cedex, Poitiers, France Abstract Strong reduction of extra-framework iron ions was attempted by sodium azide to form metallic iron particles with dimensions of a few nanometers. Na-X and Na-Y zeolites were partially ion exchanged to 5 wt % Fe content. The iron-zeolites were mixed with sodium azide, evacuated at 550 K and heated to 800 K in nitrogen to form sodium vapour by decomposing NaN3. The sodium exerts strong reduction, a part of iron can be reduced to zerovalent state to form particles in the nanometer size range, as in situ Miissbauer spectroscopy, AC susceptibility, X-ray diffraction and transmission electron microscopy studies revealed. Simultaneous partial recrystallization of the zeolite is also observed. 01999 Acta Metallurgica Inc. INTRODUCTION Zeolites may provide an appropriate hosting media for stabilising high dispersion metallic phase in nanometer size region. For preparation, as a possible way, strong reduction of extra- framework ions can be suggested. The method was attempted for iron, eg. by using sodium vapour: at 1066 K (I), and at lower temperature (673 K) with prolonged periods (5 - 48 h) (2); a part of iron ions was reduced to metallic state in both cases. To attain the same reducing effect the “local generation” of sodium vapour can also be suggested by decomposing sodium azide in a mixture: 2 Fe3+-Z + 6 NaN3 + 2 Fee-Z + 6 Na+ + 9 N2 t11 where -Z refers to the X or Y zeolite matrix. It is supposed that the reduction may proceed in the cages, at a temperature exceeding slightly that necessary to decompose NaN3, and the metallic particles formed are retained in the cages. In fact, upon the decomposition of sodium azide Na43+, Nag5+ and Naxo clusters are formed (3); they have the capability for reduction. In the present work we report on the results of the attempted reduction of iron in Fe-X and Fe-Y by Eq. 111. Methods of X-ray diffraction (XRD), AC susceptibility, in situ Mossbauer spectroscopy and transmission electron microscopy (TEM) are used for characterisation of the products. 155